Explanation:

- Option 1: Sachchidananda Sinha

- Sachchidananda Sinha was the interim president of the Constituent Assembly of India.

- He presided over the inaugural meeting on December 9, 1946.

- This is the correct answer.

- Option 2: P. Upendra

- P. Upendra was an Indian politician but not associated with the Constituent Assembly.

- He doesn't have any direct relevance to the inauguration.

- Option 3: B.R. Ambedkar

- B.R. Ambedkar was the Chairman of the Drafting Committee.

- He played a pivotal role in shaping the Indian Constitution.

- Option 4: Dr. Rajendra Prasad

- Dr. Rajendra Prasad was later elected as the permanent President of the Assembly.

- He wasn't the presider of the inaugural meeting.